Negative advertising campaigns are always entertaining, regardless of the companies involved, but when it involves Google and Microsoft, there's a whole new level of interest.

On Thursday, Feb. 7, software giant Microsoft kicked off a new national campaign designed to encourage users to ditch Google's Gmail service and switch to its own Microsoft Outlook facilities. The message of the campaign is based on privacy concerns.

Microsoft's new campaign is called "Don't Get Scroogled by Gmail," and raises an issue that caused concerns on numerous occasions: the fact that Google scans users' e-mails so it can target and tailor advertising to accompany each email message.

From now on, Microsoft will display television, print, and online advertisements with the word "Scroogled!" written in the colors of Google's logo. Subtle, right?

According to Microsoft, its new campaign against the search giant aims to "educate Americans about Google's practice of going through the contents of all Gmail emails to sell and target ads."

Moreover, the Redmond software guru also said that a study it commissioned revealed that 70 percent of consumers were unaware that e-mail providers "routinely" read personal emails for advertising purposes. Once they know, 88 percent of users "disapprove" of this practice, added Microsoft.

"Google goes through every Gmail that's sent or received, looking for keywords so they can target Gmail users with paid ads," warns Microsoft. "And there's no way to opt out of this invasion of your privacy."

Things, however, don't end here, as Microsoft has also launched a petition to "stop Google going through your emails to sell ads," and at the time of writing it has already raised nearly 300 signatures out of a target of 25,000.

"Emails are personal - and people feel that reading through their emails to sell ads is out of bounds," Stefan Weitz, Microsoft's senior director of Online Services, said in the press release. "We honor the privacy of our Outlook.com users, and we are concerned that Google violates that privacy every time an Outlook.com user exchanges messages with someone on Gmail. This campaign is as much about protecting Outlook.com users from Gmail as it is about making sure Gmail users know what Google is doing."

Meanwhile, Google has long insisted that its automatic scanning technology had no impact on user privacy, because no humans ever read account or e-mail information. Google justifies its advertising practices as a means to keep services free of charge, and claims that as long as the e-mail scanning is done automatically and no humans are involved, users need not fear about their privacy. Who is right? Google or Microsoft?